Optical Combiner for Night Vision Goggles Vignetting
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Solution Overview
Problem
Existing optical devices for superimposing electronic images onto external scenery images, such as in night vision goggles, face challenges in maintaining high external scenery transmission and minimizing field disturbance, particularly in ensuring excellent optical transmission and large depth of field while avoiding vignetting.
Innovation Solution
An optical device with a combiner formed of two optical parts assembled via an approximately plane common face, inclined at 45 degrees, featuring a weakly reflective coating and an optical relay that provides an intermediate image in the focal plane, allowing the pupil image to coincide with the objective aperture and preventing vignetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple beam-splitting plate is used as the optical combiner, then the device structure is simple, but the optical transmission of the external scenery is not excellent enough and field disturbance occurs
Solution Approach 1:
The combiner is divided into two separate optical parts (a first optical part and a second optical part) that are assembled together via a common face. This segmentation allows each part to have optimized optical properties - the first part transmits external scenery light while the second part reflects electronic image light, resolving the contradiction between structural simplicity and optical transmission quality.
Solution Approach 2:
Different regions of the combiner are given different optical properties. The common face has a specific reflectivity (5-20%) optimized for electronic image reflection, while the other faces are designed for maximum transmission of external scenery. This local optimization of optical properties ensures excellent overall transmission while maintaining the beam-splitting function.
2Object-affected harmful factors
If a small-sized reflecting surface is used in the combiner, then field disturbance is minimized, but the pupil image cannot coincide with the objective aperture causing vignetting
Solution Approach 1:
The combiner is designed as a three-dimensional assembly of two optical parts with a common face, rather than a simple two-dimensional plate. This dimensional complexity allows the pupil image to be positioned at a specific depth where it coincides with the objective aperture, eliminating vignetting while keeping the reflecting surface size controlled to minimize field disturbance.
Solution Approach 2:
The common face acts as an intermediary between the first and second optical parts. Its specific reflectivity (5-20%) serves as a mediator that allows partial transmission of electronic image light while maintaining the primary function of transmitting external scenery light, thus resolving the conflict between minimizing field disturbance and maximizing visual field.
3Manufacturing precision
If the combiner is positioned to achieve large depth of field, then objects at various distances can be viewed, but optical transmission and field disturbance are compromised
Solution Approach 1:
By segmenting the combiner into two optical parts with a common face, the system achieves large depth of field through the specific geometric arrangement and optical properties of the assembly, while each segment maintains optimized transmission characteristics that prevent degradation of overall optical transmission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution ensures high external scenery transmission (>90%) while minimizing field disturbance, allowing for a large visual field and effective superposition of electronic images without vignetting, enhancing pilot comfort and safety during night missions.
Implementation Method 1
the common face has a weakly reflective coating, the reflection coefficient of this coating being less than 10% in the spectral band used by the photosensitive surface
Implementation Method 2
the opposing face has approximately the form of a reflecting spherical surface
Implementation Method 3
a collimation optic 21
Data Source
AI summary
The field of the invention is that of optical devices allowing the superposition of an electronic image on an image coming from an external scenery. The subject of the invention is an optical device for superposing images, designed to be positioned in front of an optical module comprising at least an objective and a photosensitive surface positioned in the focal plane of said objective. The device comprises an image source, an optical relay and an optical combiner formed of two optical parts assembled via an approximately plane common face including a weakly reflective coating. The combiner has the general form of a plate with plane parallel faces, the common face being inclined at around 45 degrees to said plane faces. It has an entrance face and a opposing face that are approximately perpendicular to the plane faces, the opposing face having approximately the form of a reflecting spherical surface. This device applies in particular to night vision goggles where, when the optical combiner is placed in front of the objective of a goggles body, it allows superposition of an electronic image on the external scenery while introducing marginal attenuation.